1. Field of the Invention
The present invention generally relates to magnetic recording media, and, more particularly, to a magnetic recording medium that can achieve a higher signal to noise ratio (S/N ratio) and a higher recording density.
2. Description of the Related Art
In general, circular magnetic disks are widely spread as magnetic recording media used in computers, because a random access can be made to circular magnetic disks. Particularly, magnetic disks having substrates made of a hard material such as aluminum or glass are used. Conventionally, a Cr underlayer is formed on a non-magnetic substrate such as an aluminum substrate, and a magnetic recording layer made of a magnetic alloy containing Co as a main component is formed on the Cr underlayer. Magnetic signals supplied through a magnetic head are recorded on the magnetic recording layer.
In recent years, there has been an increasing demand for higher-density magnetic disks. To achieve higher-density magnetic disks, the noise level of the magnetic recording medium should be lowered, and the S/N ratio should be increased. Therefore, it is necessary to reduce the magnetic particle diameter and to break the magnetic interrelation between magnetic particles. Also, alloys having various compositions containing Co as a main component have been developed. To realize a magnetic recording medium having a density higher than 10 Gb/inch2, the coercivity of the magnetic recording layer needs to be increased, while the noise of the magnetic recording layer needs to be reduced. U.S. Pat. No. 5,523,173 discloses a CoPtCrB alloy thin film as a material that satisfies the above conditions.
U.S. Pat. No. 5,523,173 specifies a preferred composition of the magnetic recording layer, such as, a composition containing 4 atm % (atomic percent) to 12 atm % of platinum (Pt), 18 atm % to 23 atm % of chromium (Cr), and 2 atm % to 10 atm % of boron (B). However, a high recording resolution is required for achieving a recording density of 10 Gb/inch2 or higher in the longitudinal-direction recording so as to satisfy the demand for higher-density recording. To obtain a high recording resolution, the magnetic recording layer needs to be thinner.
The magnetic recording layer having the above composition, however, is liable to have a low saturation magnetization due to higher-concentration Cr and noise. As a result, in a conventional magnetic recording medium having such a thinner magnetic recording layer, the output of reproduction signals is not sufficient.
A general object of the present invention is to provide magnetic recording media in which the above disadvantages are eliminated.
A more specific object of the present invention is to provide a high-density, low-noise magnetic recording medium.
The above objects of the present invention are achieved by a magnetic recording medium comprising: a substrate; a non-magnetic underlayer formed on the substrate; and a magnetic recording layer formed on the underlayer. In this magnetic recording medium, the magnetic recording layer contains cobalt as a main component, 10 atm % to 18 atm % of chromium, 5 atm % to 20 atm % of platinum, and 10 atm % to 20 atm % of boron.
In the above structure, the concentration of boron is higher than in the prior art, while the concentration of chromium is lower than in the prior art. Thus, noise is lowered, and high-density recording can be achieved.
The above objects of the present invention are also achieved by a magnetic recording device that includes a magnetic recording medium comprising: a substrate; a non-magnetic underlayer formed on the substrate; and a magnetic recording layer formed on the underlayer. In thus magnetic recording device, the magnetic recording layer contains cobalt as a main component, 10 atm % to 18 atm % of chromium, 5 atm % to 20 atm % of platinum, and 10 atm % to 20 atm % of boron.